JP6679327B2 - Ultrasonic device - Google Patents

Description

  The present invention relates to an ultrasonic device that acquires information on a subject using ultrasonic waves.

  As one of the optical imaging techniques, photoacoustic tomography (PAT) has been proposed in recent years. When the measurement light such as a pulse laser is applied to the subject, an acoustic wave is generated when the measurement light is absorbed in the subject. This phenomenon is called a photoacoustic effect, and an acoustic wave generated by the photoacoustic effect is called a photoacoustic wave.

  The tissues constituting the subject have different absorption rates of light energy, so that the sound pressures of the generated photoacoustic waves are also different. In photoacoustic tomography, the generated photoacoustic wave is detected by a probe and the received signal is analyzed, so that information about the optical characteristics in the subject can be imaged.

  On the other hand, ultrasonic imaging is known as a method of acquiring structural information in the subject. In ultrasonic imaging, ultrasonic waves are transmitted to a subject from a plurality of ultrasonic probes arranged on a probe, and reflected waves generated at interfaces having different acoustic impedances in the subject are received and analyzed. This makes it possible to image information (structural information) on the acoustic characteristics of the subject.

  Research on a device that combines these technologies to generate photoacoustic waves (ultrasonic waves) by irradiating an ultrasonic wave generation member arranged outside the subject with light and perform ultrasonic imaging using this photoacoustic wave It is being advanced. This technology uses a photoacoustic-induced ultrasonic imaging device to distinguish it from ordinary pulse-echo type ultrasonic imaging in which ultrasonic waves electrically generated by an acoustic wave (ultrasonic wave) transmission element are used as transmission waves. be called.

  Non-Patent Document 1 describes a photoacoustic induction ultrasonic imaging apparatus using a micro spherical light absorber as an ultrasonic wave generation member.

Thomas Felix Fehm, Xose Luis Dean-Ben, Daniel Razasky, 'Hybrid optoacoustic and ultrasound imaging in three dimensions and real time by optical excitation of a passive element', Proceedings of SPIE Vo. 9323, 93232X-1

  In a normal pulse echo type ultrasonic imaging apparatus having a plurality of probes for transmitting ultrasonic waves, the voltage is changed for each probe to arbitrarily change the intensity distribution of ultrasonic waves to be irradiated on the subject. can do.

  On the other hand, with the ultrasonic wave generation method described in Non-Patent Document 1, the intensity distribution of ultrasonic waves could not be adjusted.

  Therefore, the present invention, in the photoacoustic induction ultrasonic imaging apparatus, to generate an ultrasonic wave having a desired intensity distribution, or an ultrasonic device capable of making the intensity distribution of the generated ultrasonic wave close to the desired intensity distribution. The purpose is to provide.

Ultrasonic device of the present invention includes a probe for converting into an electric signal by receiving the ultrasonic waves, the absorption of light planar ultrasonic generation region including an absorber to have a plane distribution super A sound wave generating member, and a light irradiation unit arranged to irradiate the ultrasonic wave generation region with light , the absorber, from the in-plane distribution of the intensity of light irradiated to the ultrasonic wave generation region. to generate ultrasonic waves having an in-plane distribution of even small sound pressure, before Symbol ultrasonic generation region is characterized by functioning as a surface sound source.

  According to the present invention, in a photoacoustic induction type ultrasonic imaging apparatus, an ultrasonic device capable of generating an ultrasonic wave having a desired intensity distribution or making the generated ultrasonic wave intensity distribution closer to a desired intensity distribution. Can be provided.

The figure explaining the structure of the photoacoustic measuring device which concerns on embodiment. The figure explaining the structure of the sound generation member which concerns on embodiment. Flowchart of measurement according to the embodiment Schematic diagram of an ultrasonic wave generation member according to a modification

  Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the drawings. In principle, the same components are designated by the same reference numerals, and duplicate description will be omitted. The ultrasonic device of the present embodiment includes an ultrasonic wave generating member having an absorber that generates ultrasonic waves by light irradiation, and irradiates the subject with ultrasonic waves generated by irradiating the ultrasonic wave generating member with light. By doing so, the information of the subject is acquired. The absorber of the present embodiment generates planar ultrasonic waves. Therefore, it is possible to suppress the attenuation of the ultrasonic wave until it is irradiated onto the subject, rather than generating the spherical wave ultrasonic wave. In addition, the ultrasonic wave generation member has an in-plane distribution of the light absorptance in the irradiation region where the light is irradiated. Thereby, it is possible to generate an ultrasonic wave having an intensity distribution different from the intensity distribution of the light with which the irradiation area is irradiated. For example, when it is desired to generate a planar ultrasonic wave having a uniform intensity as much as possible, if an ultrasonic wave generation member having a distribution of absorptance that cancels unevenness in light irradiation is used, unevenness in intensity is more uneven than unevenness in light irradiation. It is possible to generate a small ultrasonic wave.

  In the present invention and the present specification, an acoustic wave generated from a light absorber of a subject (including both the inside and the surface) by light irradiation is referred to as a photoacoustic wave, and is obtained by converting the photoacoustic wave. The electric signal is called a photoacoustic wave signal. An image obtained by reconstructing a photoacoustic wave signal is called a photoacoustic image. On the other hand, a photoacoustic wave (ultrasonic wave) generated from the ultrasonic wave generation member by light irradiation and transmitted to the subject is called a transmitted ultrasonic wave, and is reflected or scattered by the subject (including both the inside and the surface). The transmitted ultrasonic wave is referred to as a reflected wave. An electric signal obtained by converting the reflected wave is called an ultrasonic signal, and an image obtained by reconstructing the ultrasonic signal is called an ultrasonic image.

  Hereinafter, embodiments of the present invention will be described in more detail.

  In the present embodiment, a subject information acquisition apparatus that can perform not only the above-described photoacoustic-induced ultrasonic imaging but also photoacoustic tomography will be described. In the present embodiment, the transmitted ultrasonic waves reflected or scattered by the subject are received and converted by the probe, and acoustic characteristic value distribution information inside the subject is acquired based on the acquired ultrasonic signals. , Photoacoustic induction ultrasonic imaging is performed by visualizing (imaging). Note that the acoustic characteristic value distribution information generally means distribution data having a sound pressure distribution, an acoustic impedance difference distribution, a scattering intensity distribution, a sound velocity distribution, an acoustic attenuation distribution, or values related thereto. In the present embodiment, the subject is irradiated with pulsed light, the photoacoustic wave generated in the subject due to the pulsed light is received by the probe, converted, and based on the acquired photoacoustic wave signal. Photoacoustic tomography is performed by acquiring and visualizing information related to the optical characteristics of the subject. The information related to the optical characteristics is generally the initial sound pressure distribution in the subject, the light absorption energy density distribution, the absorption coefficient distribution, or the characteristic distribution related to the concentration of the substance constituting the tissue. . The characteristic distribution related to the concentration includes, for example, a distribution of oxygen saturation, total hemoglobin concentration, oxyhemoglobin concentration, deoxyhemoglobin concentration, or the like. Further, distributions such as glucose concentration, collagen concentration, melanin concentration, fat and water volume fraction may be used. The subject information acquisition apparatus according to this embodiment is one form of an ultrasonic apparatus. In the present invention and this specification, an apparatus that does not perform photoacoustic tomography is called an ultrasonic apparatus as long as the object is irradiated with ultrasonic waves and information about the object is acquired.

(System configuration)
The configuration of the subject information acquiring apparatus according to this embodiment will be described with reference to FIG. The subject information acquisition apparatus according to the present embodiment includes a light source 103, a probe unit 101 having a plurality of probes 102, an acoustic wave processing unit 108, an ultrasonic wave generation member 104, a subject holding member 107, and a device control unit. It comprises 109. The pulsed light emitted from the light source 103 is guided by the optical transmission path, reaches the ultrasonic wave generation member 104, and generates ultrasonic waves. At least a part of this ultrasonic wave (transmitted ultrasonic wave) is transmitted to the subject. The transmitted ultrasonic waves that have propagated through the inside of the subject held by the subject holding member 107 are reflected and scattered when irradiated to the ultrasonic scatterer inside the subject, and a reflected wave is generated. The reflected wave is received by the probe 102 of the probe unit 101, converted into an electric signal, and the electric signal is processed by the acoustic wave processing unit 108 and the device control unit 109 to obtain ultrasonic image data (acoustic wave) of the subject. Characteristic value distribution information data) is acquired. When performing the photoacoustic wave imaging, the absorber 111 of the ultrasonic wave generation member 104 is retracted from the optical path between the subject and the light irradiation unit 5 and is generated by irradiating the subject with pulsed light. The photoacoustic wave is received and converted by the probe 102 to obtain a photoacoustic wave signal. Then, the photoacoustic wave signal is processed by the acoustic wave processing unit 108 and the device control unit 109 to acquire photoacoustic image data (optical characteristic information data) of the subject. The ultrasonic image data and the photoacoustic image data thus obtained are imaged and displayed on the display device.

  Hereinafter, each component of the subject information acquisition apparatus according to the present embodiment will be described in more detail.

(Probe unit)
Reference numeral 101 is a unit that has and holds the probe 102. The subject information acquiring apparatus of this embodiment includes a hemispherical probe unit 101 as shown in FIG. 1, and a plurality of probes 102 are arranged on the inner surface thereof. FIG. 1B is a schematic view of the subject information acquisition apparatus according to the present embodiment as observed from above in the vertical direction (Z-axis direction). On the probe unit 101, 512 probes 102 are spirally arranged at positions along the hemispherical surface.

  A light irradiation unit 105 is provided on the bottom of the probe unit 101 so that the subject can be irradiated with the pulsed light 106 in the Z-axis direction.

  In the present embodiment, the light irradiation unit 105 is an opening, and the light from the light transmission path that transmits the light from the light source 103 is emitted.

  The probe unit 101 is configured to be movable along the XY plane by an XY stage (not shown). By doing so, irradiation of pulsed light and reception of reflected waves and photoacoustic waves can be performed at a plurality of positions with respect to the subject, and measurement accuracy can be improved. The space between the holding member 107 and the probe unit 101 is filled with an acoustic matching material that serves as an acoustic matching layer. The acoustic matching material is, for example, a liquid or gel, and in this embodiment, water is used. The ultrasonic wave generation member 104 can move integrally with the movement of the probe unit 101. The probe unit is not limited to this configuration as long as the probe held by the probe unit can receive the reflected wave and convert the reflected wave into an electric signal. For example, it may have a planar shape and the probes may be arranged on a flat surface. Generally, a plurality of probes 102 arranged one-dimensionally or two-dimensionally is used. By using such a multidimensional array element, reflected waves and photoacoustic waves can be detected at a plurality of locations at the same time, the detection time can be shortened, and the influence of vibration of the subject can be reduced.

(Probe)
The probe 102 is means for detecting a reflected wave and a photoacoustic wave coming from the subject and converting them into an electric signal (ultrasonic wave signal or photoacoustic wave signal). The probe 102 is also called an ultrasonic probe, an acoustic wave probe, an acoustic wave detector, or a transducer. In the present embodiment, the probe 102 needs to detect both the reflected wave of the transmitted ultrasonic wave and the photoacoustic wave and convert it into an electric signal.

  The frequency of the photoacoustic wave generated from the living body is 100 KHz to 100 MHz. On the other hand, the frequency of the transmitted ultrasonic wave is determined by the thickness of the sound generating member and is, for example, 8 MHz or less. For the probe 102, an ultrasonic detector capable of receiving the above frequency band is used. Specifically, a conversion element using piezoelectric ceramics (PZT), a conversion element using optical resonance, or a capacitance type CMUT (Capacitive Micromachined Ultrasonic Transducer) can be used. In this embodiment, a CMUT is used as the probe 102. The probe 102 preferably has high sensitivity and a wide frequency band. In this embodiment, as the probe 102, a single element having a 3 mm opening and a band of 0.5-5 MHz is used. By ensuring the sensitivity in the low frequency band, it is possible to prevent hollowing out even in a relatively thick blood vessel of about 1-3 mm.

(Acoustic wave processing unit)
The acoustic wave processing unit 108 is a unit that includes an amplifier, an A / D converter, and the like, amplifies the electric signal converted by the probe 102, and converts the electric signal into a digital signal. The converted signal is transmitted to the device control unit 109. In the present embodiment, the sampling frequency of the acoustic wave processing unit 108 is 20 MHz, and the sampling number is 2048. The output data is a signed 12-bit data.

(Ultrasonic wave generation member)
The ultrasonic wave generation member 104 for generating the transmitted ultrasonic wave is arranged between the probe unit 101 and the subject holding member 107. The ultrasonic wave generation member 104 can be installed in the light irradiation range by the drive mechanism 110. The ultrasonic wave generating member 104 may be attached to the arm and the ultrasonic wave generating member may be arranged by moving the arm.

  2A and 2B show the configuration of the ultrasonic wave generation member 104. In the ultrasonic wave generation member 104, the absorber 111 is arranged on the film 202 having a substantially flat structure. The film 202 is a support member for the absorber 111, and is a sheet-shaped support member (referred to as a sheet member) in the present embodiment. The film 202 preferably has high transmittance of ultrasonic waves (transmitted ultrasonic waves and reflected waves). This is because the generated transmitted ultrasonic waves are reflected by the subject, and the reflected waves again reach the probe 102 via the ultrasonic wave generation member 104. Therefore, it is desirable to use a material having a high ultrasonic wave transmittance such as polyethylene terephthalate, nylon, vinyl, polycarbonate, acrylic, or rubber. The thickness is preferably about 50-500 um and thin.

  The absorber 111 can be produced, for example, by applying a pigment ink, a dye ink, or a resin ink to the film 202 with an inkjet printer or the like. Examples of the pigment material include black pigments such as carbon black and cyan pigments such as copper phthalocyanine. Alternatively, a metal such as gold, silver or aluminum may be deposited. Further, a compound such as titanium oxide may be added as a scatterer. Alternatively, the absorber may be applied to the film 202 and heated to diffuse the absorber inside the film. When the absorber is on the surface of the film, since the absorber layer is thin, it is possible to generate broadband transmission ultrasonic waves including high frequencies. On the other hand, when the thickness of the absorber layer is increased by diffusing it inside, low-frequency transmission ultrasonic waves are generated according to the absorber layer thickness. By laminating the films, it is possible to generate lower frequency transmission ultrasonic waves. The transmitted ultrasonic wave may be generated so as to include a frequency within a band that can be received by the probe 102, and if a frequency in an unnecessary band is included, it becomes noise.

  FIG. 2B shows an irradiation region 203 of the pulsed light 106. An area that receives the pulsed light and actually generates an ultrasonic wave (hereinafter, referred to as a transmitted ultrasonic wave generation area) is an area of the absorber 111 that receives the pulsed light, and the absorber 111 and the irradiation area 203. This is the area where and overlap. In the case of the present embodiment, as shown in FIG. 2B, the absorber 111 is included in the irradiation region 203, so that the entire absorber 111 is the transmission ultrasonic wave generation region.

The ultrasonic wave generation member 104 of this embodiment functions as a surface sound source. However, that the ultrasonic wave generation member functions as a surface sound source means that the transmission ultrasonic wave generation region, which is a region in which ultrasonic waves are actually generated, of the ultrasonic wave generation member functions as a surface sound source. In the present invention, and herein, as long as more than 10 times the width w _a height h of the transmission ultrasonic wave generating region, regarded as the transmitted ultrasonic wave generation region it serves as a surface sound source. The width w _a and the height h of the transmission ultrasonic wave generation region will be described with reference to FIGS. 2B and 4A. As shown in FIG. 2B, the plane when the transmission ultrasonic wave generation region is viewed from the light source is the xy plane. The z-axis is the depth direction of the paper and corresponds to the optical axis. At this time, the transmission to the width w _a of the ultrasonic generation region, refers to the width in the width and y-axis direction in the x-axis direction, both the width in the width and y-axis direction in the x axis direction, the height h If it is 10 times or more, it is considered that the transmission ultrasonic wave generation region functions as a surface sound source. When the transmission ultrasonic wave generation region is circular as shown in FIG. 2B, the width w _a is the diameter. Further, the height h of the transmission ultrasonic wave generation region refers to the length of the transmission ultrasonic wave generation region in the optical axis direction (z axis). More specifically, as shown in FIG. 4A, it refers to the length between the surface on the light source side and the surface on the opposite side of the light source in a plane parallel to the z axis. When the transmission ultrasonic wave generation region is flat as in the present embodiment, the height of the transmission ultrasonic wave generation region matches the thickness of the absorber. On the other hand, as shown in FIG. 4B, when the transmission ultrasonic wave generation region has a curvature, the height h of the transmission ultrasonic wave generation region is larger than the thickness of the absorber, but the width w _a is thick. If it is 10 times or more of h, the transmission ultrasonic wave generation region functions as a surface sound source.

  By the way, a method of transmitting an ultrasonic wave to the subject by using another linear probe or the probe 102 of the probe unit 101 without using the ultrasonic wave generating member 104 and acquiring an ultrasonic image is also conceivable. In these cases, another linear probe is required, or an ultrasonic wave transmission function must be added to the probe unit, which increases the cost. Therefore, there is an advantage in using the ultrasonic wave generation member 104. In particular, in the case of an ultrasonic device that also performs photoacoustic wave measurement as in the present embodiment, ultrasonic measurement can be performed by adding an ultrasonic wave generation member to the configuration required for photoacoustic wave measurement.

(In-plane distribution of absorber)
In the ultrasonic wave generation member 104, the light irradiation region 203 has regions having different light absorptances. In addition, in the subject information acquisition device of this embodiment, the absorber 111 in the irradiation region 203 has regions having different absorption rates. When the intensity of the light applied to the irradiation region 203 is not uniform, it is desirable that the in-plane distribution of the absorber 201 in the light irradiation region 203 is arranged so as to reduce the intensity distribution of the irradiation light. In the irradiation region 203 of this apparatus, the beam profile of the irradiation light has a Gaussian-shaped intensity distribution. That is, if the in-plane distribution of the absorptance of the absorber is uniform, the intensity distribution of the transmitted ultrasonic wave becomes a Gaussian-shaped intensity distribution.

  Here, the generation of transmitted ultrasonic waves will be described. The sound pressure P of the transmitted ultrasonic wave is represented by the equation (1) like the normal photoacoustic wave.

  Γ is a Gruneisen coefficient which is an elastic characteristic value, and is a product of the square of the volume expansion coefficient (β) and the sound velocity (c) divided by the specific heat (Cp). μ is the absorption coefficient of the absorber, and is the light absorption coefficient at the central wavelength of the pulsed light 106 to be irradiated. Φ is the amount of light in a local region (the amount of light applied to the absorber), which is a function having a distribution on the xy plane. If the absorption coefficient distribution of the absorber in the irradiation area 203 is an absorption coefficient distribution that is the reciprocal of the in-plane distribution Φ of the light quantity, it is possible to cancel the intensity unevenness of the light quantity, and transmit ultrasonic waves having a uniform sound pressure. Can be generated. The absorber 111 shown in FIG. 2 has an inverse Gaussian-shaped absorptance distribution. The distribution of the absorptance can be obtained, for example, by controlling the density of the applied ink with an inkjet printer or the like. Note that it may be difficult to accurately set the absorption coefficient distribution of the absorber to an inverse function of Φ, or it may be difficult to accurately align the relative position between the absorber and the light source (irradiation unit 105). In the form, it is sufficient if the distribution of the sound pressure of the transmitted ultrasonic waves can be made close to uniform. It suffices that the intensity distribution of the sound pressure of the transmitted ultrasonic wave to be generated has less intensity unevenness than the in-plane distribution Φ of the light amount in the irradiation region. Note that the standard deviation can be used as a standard for evaluating the strength unevenness. It is desirable that the variation in the intensity of sound pressure is 10% or less (the minimum value and the maximum value are within the range of 0.9 times or more and 1.1 times or less of a certain value).

  In addition, it is desirable that a region of the film 202 other than the absorber is a reflective member. When using an in-plane distribution Φ of a light amount having a weak light intensity in the peripheral portion, such as a Gaussian-shaped beam, sufficient light transmission ultrasonic waves cannot be generated with the light amount in the peripheral portion. Therefore, the transmitted acoustic wave generated in the peripheral portion cannot be used for reconstruction and becomes noise. By providing the reflection member around the absorber, the light in the peripheral portion is incident on the reflection member and generates almost no ultrasonic waves, so that noise can be reduced. The material of the film 202 may have a reflective property or may be coated with a reflective film, but a material having a low absorption coefficient so that photoacoustic waves are hardly generated is desirable. Specifically, it is desirable that the absorption coefficient is 0.001 / mm or less. When the film itself has a reflection characteristic, the absorber arranged on the film is arranged so as to come to the light irradiation unit 105 side. Further, such a reflective film may be coated so that transmitted ultrasonic waves are generated in a region smaller than the beam irradiation region. This is to obtain transmitted ultrasonic waves with a certain intensity.

  When the film 202 is a transparent film, a part of the pulsed light is transmitted to the subject side, is absorbed by the subject, and becomes a photoacoustic wave, which becomes a noise source. Here, a reflection film is coated, and a region smaller than the beam irradiation region 203 is set as a transmission ultrasonic wave generation region. For example, if the diameter of the beam is 50 mm, the transmission ultrasonic wave generation area is 40 mm.

  By the way, when the surface with the absorber is arranged on the subject side, the sound generating member 104 is more preferable because the transmitted ultrasonic waves can be transmitted without propagating in the sound generating member 104. Further, in the present invention, the ultrasonic wave generating member 104 is placed above the probe unit 101 because there is a degree of freedom in the arrangement of the drive mechanism 110. However, it is more preferable that the ultrasonic wave generating member 104 is arranged at the bottom of the hemispherical probe unit 101. This is because the sound generation member 104 does not interfere with the sound ray of the reflected wave from the subject received by the probe 102. The ultrasonic wave generation member 104 may be composed of a plurality of sheet members. For example, a sheet member supporting the absorber and a sheet member having a characteristic of reflecting pulsed light may be stacked, or a sheet member in which the absorber is arranged in a different region may be stacked. Good.

(Subject holding member)
The subject holding member 107 is a means for holding the subject, and is an arc-shaped member installed in the opening of the apparatus housing in the present embodiment. The subject holding member 107 is supported by the support member 112.

  In the present embodiment, measurement of photoacoustic wave is also performed. Therefore, the subject holding member 107 is preferably a member having a high light transmittance in order to transmit the light with which the subject is irradiated. Moreover, in order to transmit the photoacoustic wave and the reflected wave coming from the subject, it is preferable to use a material having an acoustic impedance close to that of the subject. Further, strength is required to hold the subject. Examples of such materials include polyethylene terephthalate, polymethylpentene, polyethylene and the like. When the photoacoustic wave is not measured, the light transmittance of the holding member 107 does not matter. Further, the subject holding member 107 has a function of holding the subject during measurement to reduce vibration and deformation of the subject and protecting the probe unit 101 from the subject. If is unnecessary, the subject holding member 107 is unnecessary.

(light source)
The light source 103 is a device that generates the pulsed light 106 with which the subject ultrasonic wave generation member 104 is irradiated. Further, the light source 103 generates pulsed light 106 for irradiating the subject during photoacoustic wave measurement.

  The light source 103 is preferably a laser light source in order to obtain a large output, but a light emitting diode, a flash lamp, or the like can be used instead of the laser. When a laser is used as the light source 103, various solid lasers, gas lasers, dye lasers, semiconductor lasers, and the like can be used. The irradiation timing, waveform, intensity, etc. are controlled by the device control unit 109. Instead of the device control unit 109, a light source control unit integrated with the light source 103 may control.

  The wavelength of the pulsed light 106 is a wavelength absorbed by the absorber 111 of the ultrasonic wave generation member 104. When performing photoacoustic wave measurement as in the present embodiment, the wavelength of the pulsed light 106 is a specific wavelength that is absorbed by a specific component of the components that form the subject, and the light is transmitted to the inside of the subject. Is a wavelength that propagates. Specifically, when the subject is a living body, it is desirable that the wavelength is 700 nm or more and 1100 nm or less. Further, in order to effectively generate ultrasonic waves or photoacoustic waves, light is irradiated for a sufficiently short time depending on the thermal characteristics of the ultrasonic wave generating member or the subject. When the subject is a living body, in order to effectively generate the photoacoustic wave, the pulse width of the pulsed light generated from the light source 102 is preferably about 10 nanoseconds to 50 nanoseconds. Further, since the pulse width for effectively generating the transmitted ultrasonic wave depends on the material of the ultrasonic wave generating member, it can be appropriately set according to the material of the ultrasonic wave generating member. In order to effectively generate a transmission sound wave and a photoacoustic wave with one light source, a material that can use a pulse width equivalent to the pulse width of the pulsed light with which the subject is irradiated is used as the material of the ultrasonic wave generation member. Preferably.

  In this embodiment, a titanium sapphire laser which is a solid-state laser is used, and the wavelengths are 760 nm and 800 nm. The pulsed light generated by the light source 103 is irradiated onto the subject from the light irradiation unit 105 via an optical transmission path having an optical member such as a lens, a mirror, a diffusion plate, and an optical fiber. When the distance between the light source and the light irradiation unit is short, the light transmission path may not have an optical member. In addition, the light emitting portion of the light source is arranged so as to coincide with the inner wall of the probe unit or to be located inside the inner wall, and the light source can be passed from the light source to the ultrasonic wave generating member or the subject without passing through the optical transmission path. You may irradiate with pulsed light. In this case, the light emitting unit coincides with the light emitting unit of the light source.

(Device control unit)
The device control unit 109 controls each component of the subject information acquisition device. For example, the light source, the XY stage, the reception of the probe, and the relative position between the ultrasonic wave generation member and the light irradiation unit are controlled. The device control unit 109 may also be an image generation unit that acquires information related to optical characteristics and acoustic characteristics inside the subject by performing image reconstruction or the like based on the electric signal acquired by the probe 102. is there.

  The device control unit 109 is typically a workstation having an independent CPU, a main storage device, and an auxiliary storage device, and the above-described processing is performed by software stored in advance. The device control unit 109 may be hardware designed exclusively, or may be hardware shared with other means. Further, a program that implements each function may be supplied to a system or an apparatus via a network or various storage media, and one or more processors in a computer of the apparatus may read and execute the program. It can also be realized by a circuit (for example, FPGA or ASIC) that realizes each function.

  By the way, the device control unit 109 can acquire the information input by the user of the device and present the information to the user. Specifically, based on an instruction input by the user, there are changes in measurement parameters, start / end of measurement, selection of an image processing method, storage of patient information and images, analysis of data, and the like. These are performed, for example, by a combination of an image display device such as a display and an input unit such as a keyboard, or a configuration in which the image display device such as a touch panel display and the input unit are integrated.

(Image reconstruction method)
Next, a process of reconstructing an image using the acquired photoacoustic wave signal and ultrasonic wave signal will be described. Image reconstruction is performed by the device control unit 109.

  First, a process of acquiring information related to the optical characteristics in the subject based on the photoacoustic wave signal will be described. A back-projection algorithm in a three-dimensional space can be applied to such processing. For example, in the case of the UBP method (Universal Back-Projection), the initial sound pressure distribution p (r) can be obtained by the equation (2).

At this time, the term b (r ₀ , t) corresponding to the projection data is shown in Expression (3). Here, p _d (r ₀ ) is a photoacoustic wave signal detected by the detection element, r ₀ is the position of each detection element, t is time, and Ω ₀ is the solid angle of the probe.

A similar back-projection algorithm can be used in the reconstruction of the reflected wave. Considering the time taken for the transmitted ultrasonic waves to reach the inside of the subject, t is replaced with t ′ in Expression (4). r _s is the position of the sound generating member 104, and is the intersection when the perpendicular line is drawn from the reconstruction position r to the sound generating member 104. Further, c is the speed of sound. Of course, when the sound velocity of the subject and the acoustic matching liquid are significantly different, they are taken into consideration for correction.

  By the way, in the photoacoustic measurement, part of the energy of light propagating inside the living body is absorbed by an absorber such as blood, and an acoustic wave is generated from the absorber due to thermal expansion. In addition, when there is cancer in the living body, light is similarly absorbed in the new blood vessels of the cancer and photoacoustic waves are generated. As a result, it is possible to obtain the position information of the blood vessel or the cancer by reconstructing the image of the received photoacoustic wave. In addition, information such as oxygen saturation can be obtained by utilizing the difference in absorptance with respect to the wavelength of light for each substance.

  On the other hand, in the case of reconstructing the reflected wave, the energy of the transmitted ultrasonic wave propagating inside the living body is reflected / scattered at the interface between substances with different acoustic impedances, such as the interface between the normal site in the subject and the tumor. Receive the waves. Then, based on the received reflected wave, it is possible to obtain structural information related to the acoustic characteristics in the subject. As a result, it is possible to obtain structural information on the boundary surface of cancer.

  An ultrasonic device using a linear probe, for example, transmits an ultrasonic wave from a 128-element ultrasonic probe to an object to be inspected and receives an ultrasonic wave reflected inside the object to be inspected. With such an ultrasonic device, a large structure such as a tumor interface can be captured, but it is difficult to capture a small structure such as calcification. This is because for a large interface, the ultrasonic waves are specularly reflected back to the ultrasonic probe, but for a small structure, the ultrasonic waves are scattered at various angles and returned to the ultrasonic probe. Is reduced. In this method, the probe 102 is arranged in the probe unit 101. As a result, the probe 102 can receive signals at various angles. That is, in this apparatus, even a large number of the probes 102 can receive the ultrasonic waves scattered by the calcification in the breast.

(Processing flow chart)
With reference to FIG. 3, a processing flowchart when the subject information acquisition apparatus according to the present embodiment performs ultrasonic measurement and photoacoustic wave measurement will be described. Here, a case where the breast of a subject is measured as the subject will be described.

  In step S1, measurement is started. In this state, the subject inserts the breast so as to contact the holding member 107. Water, which is an acoustic matching liquid, is filled between the holding member 107 and the breast so that air does not enter. Then, when the measurement is ready, the user performs an operation to start the measurement.

  In step S2, the sound generating member 104 is placed at a desired position. The arrangement is adjusted by using the drive mechanism 110 so that the center of the light irradiation range and the center of the in-plane distribution of the optical characteristics of the ultrasonic wave generation member 104 are aligned with each other.

  Ultrasonic measurement is performed in step S3. In ultrasonic measurement, the probe 101 unit and the ultrasonic wave generation member 104 move as a unit, so the relative position between the ultrasonic wave generation member 104 and the intensity distribution of the light with which the ultrasonic wave generation member is irradiated remains fixed. is there. Each time the ultrasonic wave generation member 104 is irradiated with irradiation light, transmitted ultrasonic waves are generated and reach the subject. Then, the probe 102 receives the reflected wave reflected and scattered by the subject. The wavelength of the irradiation light may be a wavelength for performing photoacoustic measurement, or may be a dedicated wavelength for generating a transmission ultrasonic wave.

  In step S4, it is confirmed whether the desired measurement is completed. If not completed, the process returns to step S3 to perform ultrasonic measurement. When the desired measurement is completed, the process proceeds to step S5.

  In step S5, the sound generating member 104 is retracted from the light irradiation area in order to perform photoacoustic measurement.

  Photoacoustic measurement is performed in step S6. The photoacoustic measurement is performed while moving the light irradiation position on the subject on the XY stage. This is to acquire an image of a large area. Here, in order to calculate the oxygen saturation, light with two wavelengths of 760 nm and 800 nm is alternately irradiated at the same position.

  In step S7, it is confirmed whether the desired measurement is completed. If not completed, the process returns to step S6 to perform photoacoustic measurement. When the desired measurement is completed, the process proceeds to step S8.

  Image reconstruction is performed in step S8. The image reconstruction includes ultrasonic image reconstruction and photoacoustic image reconstruction. If necessary, the ultrasonic image and the photoacoustic image may be fused by image processing.

  The measurement ends at step S9. The acquired image is confirmed, and if it is a desired image, the measurement ends. Of course, when measuring the breast on the opposite side, the measurement may be continued by returning to step S1. The ultrasonic measurement and the photoacoustic measurement may be measured by independent flowcharts.

  With the above configuration, the intensity distribution of the transmitted ultrasonic wave can be changed. As a result, a desired ultrasonic image can be acquired even in an apparatus that measures a photoacoustic wave image and an ultrasonic image with the same probe unit.

(Other modifications)
In the above-described embodiment, since the ultrasonic wave generation member 104 is substantially flat, the transmission ultrasonic wave generation region is also substantially flat. However, the ultrasonic generation member 104 and the transmission ultrasonic wave generation region are shown in FIG. 4B. Thus, it may have a curvature. For example, the ultrasonic wave generated by the ultrasonic wave generating member 104 has a curvature such that it is focused at a point 20 mm from the surface of the subject. Thereby, the transmitted ultrasonic waves can be concentrated on the region of the subject to be measured.

  Further, in the above-described embodiment, the ultrasonic wave generation member 104 has an absorptance distribution that generates an ultrasonic wave having an intensity distribution in which the intensity unevenness is smaller than the intensity unevenness of the irradiation light (intensity is nearly uniform). ing. However, the absorptance distribution is not limited to this form, and may have an absorptance distribution that increases the intensity change of ultrasonic waves in the plane.

  FIG. 4C shows an example of the ultrasonic wave generation member 104 in which the ring-shaped absorber 111 is arranged. In the ultrasonic wave generating member 104, for example, an absorber 111 having a uniform absorptivity is arranged in an area having an inner diameter of 30 mm and an outer diameter of 50 mm. At this time, since the absorber 111 and the film 202 have different absorptances, the irradiation region of the ultrasonic wave generating member has a ring-shaped absorptivity distribution. An ultrasonic image obtained by irradiating a subject with planar ultrasonic waves of substantially uniform intensity images regular reflections reflected at the interface, so that it is difficult to capture scattering due to minute calcification. However, as described above, by using the ultrasonic wave generating member having the ring-shaped absorber, dark-field imaging can be performed, and even weak scattered ultrasonic waves can be easily imaged.

  Further, the ultrasonic wave generating member 104 may be used to define the irradiation range of light in photoacoustic wave measurement. In the case of the above-described embodiment, the ultrasonic wave generation member was retracted from the optical path between the ultrasonic measurement and the photoacoustic wave measurement, but by performing the photoacoustic wave measurement without retracting the ultrasonic wave generation member, It is also possible to prevent a part of the subject from being irradiated with light. Further, the in-plane distribution of the transmittance may be adjusted to obtain an arbitrary light intensity. In this case, the ultrasonic wave generating member 104 having an absorptance distribution suitable for transmitted ultrasonic waves and the ultrasonic wave generating member 104 having an absorptivity suitable for photoacoustic wave measurement are prepared and replaced by the drive mechanism 110. You may use it. By doing so, desired ultrasonic measurement and photoacoustic measurement can be performed. However, the ultrasonic wave generation member used when measuring the photoacoustic wave may be a member that hardly generates ultrasonic waves, and is composed of a region having a low light absorptance (high transmittance) and a region having a high reflectance. it can.

  Further, the ultrasonic device of the above-described embodiment performs ultrasonic measurement and photoacoustic wave measurement, but the present invention can be applied as long as it is an ultrasonic device that generates planar ultrasonic waves, for example, It can also be applied to an ultrasonic device that performs only ultrasonic measurement without performing photoacoustic wave measurement.

  Further, the ultrasonic device according to the above-described embodiment includes the subject holding member 107 having an arc shape, but the shape of the subject holding member is not limited to this. The present invention can also be applied to an ultrasonic device that does not include a subject holding member.

  Although the preferred embodiments and modifications of the present invention have been described above, the present invention is not limited to these embodiments and modifications, and various modifications and changes can be made within the scope of the invention.

103 Light Source 104 Ultrasonic Wave Generation Member 102 Probe 111 Absorber 203 Irradiation Area

Claims (9)

A probe for converting into an electric signal by receiving ultrasonic waves, and ultrasonic wave generating member including a planar ultrasonic wave generation region including an absorber to have a plane distribution in the absorption of light, the ultrasonic A light irradiation unit arranged to irradiate the generation area with light ;
The absorbent body, said to generate ultrasonic waves having an in-plane distribution of the smaller sound pressure than the in-plane distribution of the intensity of light applied to the ultrasonic wave generating region, before Symbol ultrasonic generation region, functions as a surface sound source An ultrasonic device characterized by: A probe unit including said probe and the light irradiation unit, the ultrasound system according to the ultrasonic wave generating member to claim 1, wherein the obtaining further Bei moving means for moving integrally . A reflecting member that reflects the light from the light irradiation unit ,
The reflecting member ultrasonic device of claim 1 or 2, characterized in that it is disposed around the ultrasound generating member. The ultrasonic device according to claim 3 , wherein the reflecting member and the ultrasonic wave generating member are arranged on a sheet member arranged between the light irradiation unit and the subject . The light irradiation unit forms an irradiation region on the ultrasonic wave generation member,
The ultrasonic device according to any one of claims 1 to 4 , wherein the absorber is smaller than the irradiation region. The ultrasonic device according to claim 3 , wherein the light emitted from the light irradiation unit is incident on the ultrasonic wave generating member and the reflecting member. The in-plane distribution of the absorption rate of the ultrasound generating member, the ultrasound apparatus according to any one of claims 1乃 optimum 6 characterized in that it has a ring shape. The ultrasonic device according to any one of claims 1 to 7 , wherein the ultrasonic wave generating member has a plurality of sheet members. The said light irradiation part is comprised so that the light from the light source transmitted via the optical transmission path may be emitted, The ultrasonic apparatus of any one of Claim 1 thru | or 8 characterized by the above-mentioned.

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